प्राणीशास्त्र Zoology

थोडक्यात सारांश

This topic explains how characters pass from parents to offspring. It covers Mendel's laws with monohybrid and dihybrid crosses, deviations like incomplete dominance and codominance, multiple alleles (ABO blood groups), and then linkage and crossing over, which explain why some genes do not assort independently. Examples come mainly from animals and humans, especially Drosophila.

महत्त्वाचे मुद्दे

• Gregor Mendel (father of genetics) worked on garden pea; his laws were rediscovered in 1900 by de Vries, Correns and Tschermak.
• Monohybrid ratio: F₂ phenotype 3 : 1, genotype 1 : 2 : 1. Dihybrid ratio: 9 : 3 : 3 : 1.
• Laws: dominance, segregation (purity of gametes), independent assortment.
• Incomplete dominance: heterozygote is intermediate; F₂ 1 : 2 : 1 (e.g. flower colour in Mirabilis; in animals, Andalusian fowl: black × white → blue).
• Codominance: both alleles expressed fully, e.g. AB blood group, roan cattle (red and white hairs together).
• Multiple alleles: more than two alleles at one locus in a population. ABO blood groups are controlled by three alleles: Iᴬ, Iᴮ and i. Iᴬ and Iᴮ are codominant; both are dominant over i. There are 6 genotypes and 4 phenotypes.
• Lethal genes: e.g. yellow coat colour in mice gives a 2 : 1 ratio, as homozygous yellow die (Cuénot).
• Drosophila melanogaster (fruit fly) is ideal for genetics: short life cycle (about 2 weeks), many offspring, easy to culture, clear mutant characters, only 4 pairs of chromosomes.
• T. H. Morgan (Nobel Prize 1933) studied linkage, crossing over and sex-linked inheritance (white-eye) in Drosophila.
• Linkage: genes on the same chromosome tend to be inherited together. Complete linkage – no recombinants (seen in male Drosophila); incomplete linkage – some recombinants.
• Crossing over occurs in pachytene of meiosis I between non-sister chromatids; chiasmata are the visible cross points.
• Linkage groups = haploid chromosome number (4 in Drosophila, 23 in humans).

महत्त्वाच्या संज्ञा

• Allele – alternative form of a gene.
• Locus – fixed position of a gene on a chromosome.
• Coupling phase (cis) – two dominant alleles on one chromosome (AB/ab).
• Repulsion phase (trans) – dominant alleles on different homologues (Ab/aB).
• Recombinant – offspring with a new combination of parental characters.
• Genetic (linkage) map – diagram showing the order and relative distances of genes on a chromosome (Sturtevant, 1913).
• Sex-linked inheritance – inheritance of genes on the X chromosome, e.g. colour blindness and haemophilia in humans.

सूत्रे

• Recombination frequency (RF %) = (recombinants ÷ total progeny) × 100.
• 1% RF = 1 map unit = 1 centimorgan (cM).
• Gametes from n heterozygous pairs = 2ⁿ.
• Example: test cross progeny 420 parental-type A, 400 parental-type B, 90 recombinant-type C, 90 recombinant-type D. Total = 1000. RF = (90 + 90)/1000 × 100 = 18%. Map distance = 18 cM.

५ महत्त्वाचे प्रश्न

Q1. Why is Drosophila a good material for genetic studies?

It has a short life cycle of about two weeks, gives many offspring, is easy and cheap to culture, has easily visible mutations and has only four pairs of chromosomes, including giant polytene chromosomes.

Q2. A woman of blood group A (IᴬIᴬ) marries a man of blood group B (Iᴮi). Give the possible blood groups of their children.

Gametes: woman Iᴬ only; man Iᴮ and i. Children: IᴬIᴮ (group AB) and Iᴬi (group A) in a 1 : 1 ratio.

Q3. Explain incomplete linkage with Morgan's experiment.

• Grey body, long wing (BV, dominant) × black body, vestigial wing (bv).
• F₁ female (BbVv) test-crossed with bbvv male.
• Result: about 83% parental types and 17% recombinant types (not 1 : 1 : 1 : 1).
• Shows genes are linked but crossing over gives some recombinants.
• RF about 17% → distance about 17 map units.

Q4. Describe the ABO blood group system as an example of multiple alleles.

• Gene I on chromosome 9 with alleles Iᴬ, Iᴮ, i.
• Genotypes: IᴬIᴬ, Iᴬi (A); IᴮIᴮ, Iᴮi (B); IᴬIᴮ (AB); ii (O).
• Iᴬ and Iᴮ codominant; i recessive.
• Antigens on RBC and antibodies in plasma.
• Uses: transfusion, paternity disputes.

Q5. Explain sex-linked inheritance with the example of colour blindness.

• Gene on X chromosome, recessive (Xᶜ).
• Males (XY) show the trait with one copy; females need two copies.
• Carrier mother (XXᶜ) × normal father (XY): half of sons colour-blind, half of daughters carriers.
• Criss-cross inheritance: father → daughter → grandson.
• Haemophilia follows the same pattern.

परीक्षेसाठी टीप

Show crosses with gametes and a Punnett square every time. Practise one map-distance numerical and one blood-group problem.

थोडक्यात सारांश

Evolution is the slow, gradual change in living organisms over many generations, leading to new species from older forms. This topic covers the origin of life, evidences of evolution, theories of Lamarck, Darwin and de Vries, Modern Synthetic Theory, Hardy–Weinberg principle, speciation and an outline of human evolution.

महत्त्वाचे मुद्दे

• Evolution is उत्क्रांती in Marathi.
• Origin of life: Oparin (1924) and Haldane (1929) proposed chemical evolution in a reducing atmosphere. Miller and Urey (1953) made amino acids by passing electric sparks through CH₄, NH₃, H₂ and water vapour.
• Evidences of evolution: palaeontology (fossils, e.g. horse evolution, Archaeopteryx), comparative anatomy (homologous and analogous organs, vestigial organs), embryology, biogeography, connecting links, molecular biology (DNA and protein similarity).
• Lamarckism (Philosophie Zoologique, 1809): use and disuse of organs, and inheritance of acquired characters (e.g. long neck of giraffe). Weismann disproved it by cutting tails of mice for many generations (germplasm theory).
• Darwinism (On the Origin of Species, 1859): over-production, struggle for existence, variations, survival of the fittest (term by Herbert Spencer) and natural selection. Alfred Russel Wallace reached the same idea independently.
• Mutation theory: Hugo de Vries (1901), working on Oenothera lamarckiana (evening primrose) – sudden large changes (mutations) form new species.
• Modern Synthetic Theory (Neo-Darwinism): combines Darwin with genetics; factors are gene mutation, genetic recombination, chromosomal changes, natural selection, reproductive isolation, genetic drift and gene flow.
• Industrial melanism in the peppered moth (Biston betularia) in England is a classic example of natural selection.

महत्त्वाच्या संज्ञा

• Homologous organs – same origin and structure, different function (forelimbs of man, whale, bat, cat) → divergent evolution.
• Analogous organs – different origin, same function (wings of insect and bird) → convergent evolution.
• Vestigial organs – reduced, non-functional organs (human appendix, wisdom teeth, nictitating membrane, tail bone/coccyx).
• Adaptive radiation – evolution of many forms from one ancestor in different habitats (Darwin's finches; Australian marsupials).
• Genetic drift – random change in gene frequency in small populations (founder effect, bottleneck).
• Speciation – formation of new species; allopatric (geographical separation) and sympatric (in the same area).
• Reproductive isolation – barriers that stop interbreeding between populations.

सूत्रे

• Hardy–Weinberg principle (1908): in a large, randomly mating population with no mutation, migration, selection or drift, allele and genotype frequencies remain constant.
• p + q = 1 and p² + 2pq + q² = 1 (p = frequency of dominant allele, q = recessive allele).
• Example: if 16% of a population shows a recessive trait, q² = 0.16, so q = 0.4 and p = 0.6. Heterozygotes 2pq = 2 × 0.6 × 0.4 = 0.48 (48%); homozygous dominant p² = 0.36 (36%).

५ महत्त्वाचे प्रश्न

Q1. What are homologous organs? Give an example.

Homologous organs have the same basic structure and embryonic origin but may do different jobs. Example: the forelimbs of human, whale, bat and cheetah. They show common ancestry (divergent evolution).

Q2. In a population, the frequency of the recessive allele is 0.3. Find the frequency of heterozygotes.

q = 0.3, so p = 1 − 0.3 = 0.7. Heterozygotes 2pq = 2 × 0.7 × 0.3 = 0.42, i.e. 42%.

Q3. Explain Darwin's theory of natural selection.

• Organisms produce more offspring than can survive.
• Struggle for existence (intraspecific, interspecific, environmental).
• Variations exist; some are favourable.
• Survival of the fittest; natural selection.
• Favourable variations inherited; accumulate over generations; new species arise.
• Criticism: could not explain the source of variation.

Q4. Describe the Modern Synthetic Theory of evolution.

• Proposed by Dobzhansky, Fisher, Haldane, Wright, Mayr, Huxley and others.
• Gene mutations and chromosomal changes create variation.
• Recombination during meiosis reshuffles genes.
• Natural selection changes allele frequencies.
• Reproductive isolation separates populations into species.
• Genetic drift and gene flow also act.

Q5. Give an outline of human evolution.

• Dryopithecus and Ramapithecus (ape-like ancestors, about 15 million years ago).
• Australopithecus (East Africa; walked upright).
• Homo habilis (handy man; first stone tools).
• Homo erectus (used fire; Java man, Peking man).
• Homo neanderthalensis; Homo sapiens (arose in Africa, spread worldwide).

परीक्षेसाठी टीप

For theories, write the main points as a numbered list and add one criticism. The Hardy–Weinberg numerical is a quick, sure-mark question.

थोडक्यात सारांश

Population genetics studies how often genes and genotypes occur in a population and how these frequencies change over generations. The Hardy–Weinberg law states that, without outside forces, these frequencies stay constant. Any change shows that evolution is taking place. This topic covers gene pool, allele and genotype frequencies, the Hardy–Weinberg equation with worked problems, and the factors that disturb the equilibrium.

महत्त्वाचे मुद्दे

• A population is a group of interbreeding individuals of one species in an area. The total of all alleles in it is the gene pool.
• Allele frequency = number of copies of one allele ÷ total copies of all alleles of that gene.
• The Hardy–Weinberg law was stated independently by G. H. Hardy (English mathematician) and W. Weinberg (German physician) in 1908.
• Statement: in a large, randomly mating population, allele and genotype frequencies remain constant from generation to generation if there is no mutation, migration, selection or genetic drift.
• If p = frequency of dominant allele A and q = frequency of recessive allele a, then p + q = 1.
• Genotype frequencies are p² (AA) + 2pq (Aa) + q² (aa) = 1.
• Conditions for equilibrium: very large population, random mating, no mutation, no gene flow (migration), no natural selection.
• Factors that change allele frequencies (evolutionary forces): mutation, gene flow (migration), genetic drift (chance changes, strong in small populations), natural selection and non-random mating (inbreeding).
• Genetic drift includes the founder effect (a few individuals start a new population) and the bottleneck effect (a population is drastically reduced by a disaster).
• The law is a "null model": real populations are compared with it to detect evolution.

महत्त्वाच्या संज्ञा

• Gene pool – all alleles of all genes in a population.
• Allele frequency – proportion of one allele among all alleles of a gene.
• Genetic equilibrium – state in which allele frequencies do not change.
• Gene flow – transfer of alleles between populations by migration.
• Genetic drift – random change of allele frequency by chance.

सूत्रे

• p + q = 1
• p² + 2pq + q² = 1
• q = √(frequency of recessive phenotype), when the recessive phenotype is aa only.
• Frequency of carriers (heterozygotes) = 2pq.

५ महत्त्वाचे प्रश्न

Q1. State the Hardy–Weinberg law.

In a large, randomly mating population with no mutation, migration, selection or drift, the allele frequencies and genotype frequencies remain constant generation after generation; genotype frequencies are given by p² + 2pq + q² = 1.

Q2. What is the founder effect?

When a small group of individuals leaves a population and starts a new one, the new population carries only the alleles of the founders. Its allele frequencies may be very different from the parent population, purely by chance.

Q3. In a population of 1,000 people, 160 show a recessive trait (aa). Find p, q and the number of each genotype.

1. q² = 160 ÷ 1000 = 0.16
2. q = √0.16 = 0.4
3. p = 1 − 0.4 = 0.6
4. AA = p² = 0.36 → 0.36 × 1000 = 360
5. Aa = 2pq = 2 × 0.6 × 0.4 = 0.48 → 480
6. aa = 160
7. Check: 360 + 480 + 160 = 1000 ✓

Q4. Albinism occurs in 1 in 10,000 people. What proportion are carriers?

1. q² = 1/10,000 = 0.0001
2. q = √0.0001 = 0.01
3. p = 1 − 0.01 = 0.99
4. Carriers = 2pq = 2 × 0.99 × 0.01 = 0.0198, about 1 in 50 people.
5. So carriers are far more common than affected persons; most recessive alleles hide in heterozygotes.

Q5. Explain the factors that disturb Hardy–Weinberg equilibrium.

• Mutation: adds new alleles.
• Gene flow: migration in and out.
• Genetic drift: founder and bottleneck effects; stronger in small populations.
• Natural selection: favours some genotypes (e.g. sickle-cell trait in malaria areas).
• Non-random mating: inbreeding raises homozygotes.
• Conclusion: these forces cause evolution.

परीक्षेसाठी टीप

In numericals, always start from q² (the recessive phenotype), find q, then p. Show the check step; it earns full marks and catches mistakes.

थोडक्यात सारांश

Fossils are the preserved remains or traces of organisms that lived in the past. They are the direct evidence of evolution and help us arrange the history of life on a time chart called the geological time scale. This topic covers how fossils are formed, types of fossils, methods of dating them, and the eras and periods of the geological time scale with the main animal events.

महत्त्वाचे मुद्दे

• The study of fossils is palaeontology; Georges Cuvier is called its father. Fossil is जीवाश्म in Marathi.
• Fossils usually form in sedimentary rocks, when dead organisms are quickly buried by mud or sand so that they do not decay.
• Types of fossils:
• Petrified fossils – tissues replaced by minerals such as silica (petrified wood, bones).
• Moulds and casts – a hollow impression of the body (mould) later filled by minerals (cast).
• Impressions/compressions – thin films or prints of leaves, feathers or soft bodies.
• Whole preservation – insects in amber (tree resin); woolly mammoths frozen in ice in Siberia.
• Trace fossils – footprints, burrows, and coprolites (fossil dung).
• Dating of fossils: relative dating by position in rock layers (lower layers are older); absolute (radiometric) dating using decay of radioactive elements.
• Carbon-14 dating (half-life about 5,730 years) is useful for remains up to about 50,000 years. Potassium–argon and uranium–lead methods date very old rocks.
• Earth is about 4.6 billion years old. The time scale is divided into eons, eras, periods and epochs.
• Living fossils are present-day organisms that have changed very little over long periods: Limulus (king crab), Latimeria (coelacanth), Sphenodon (tuatara).
• Connecting links such as Archaeopteryx (between reptiles and birds) show transitions between groups.

महत्त्वाच्या संज्ञा

• Half-life – time in which half of a radioactive substance decays.
• Index fossil – fossil of a widespread, short-lived species used to date rock layers.
• Mass extinction – loss of a large number of species in a short geological time.
• Stratigraphy – study of rock layers (strata).

महत्त्वाची माहिती

• The Mesozoic era is called the "Age of Reptiles"; the Cenozoic is the "Age of Mammals".

५ महत्त्वाचे प्रश्न

Q1. What are living fossils? Give two examples.

Living fossils are present-day organisms that closely resemble their fossil ancestors and have changed very little for millions of years. Examples: Limulus (king crab) and Latimeria (coelacanth fish).

Q2. Write the principle of carbon dating.

Living organisms take in carbon-14 along with carbon-12. After death, C-14 decays to nitrogen-14 with a half-life of about 5,730 years while C-12 stays constant. The C-14 : C-12 ratio in a fossil tells how long ago the organism died.

Q3. Describe the process of fossilisation and types of fossils.

• Conditions: quick burial, hard parts, sedimentary rock, absence of decay.
• Types: petrification, moulds and casts, impressions, amber, freezing, trace fossils.
• Examples of each.

Q4. Describe the geological time scale.

• Age of Earth; eons, eras, periods.
• Table of eras and periods with main events.
• Mass extinctions at end-Permian and end-Cretaceous.

Q5. Explain how fossils provide evidence of evolution.

• Fossils show simple forms in older rocks and complex forms in newer rocks.
• Connecting links: Archaeopteryx, Seymouria, therapsids.
• Fossil series: evolution of horse.
• Dating confirms the sequence.

परीक्षेसाठी टीप

Learn the order of periods with a memory line such as "Camels Often Sit Down Carefully, Perhaps Their Joints Creak" (Cambrian → Cretaceous).

थोडक्यात सारांश

Gametogenesis is the formation of male and female gametes (sperms and ova) in the gonads. Fertilisation is the fusion of a sperm and an ovum to form a diploid zygote. This topic covers spermatogenesis, oogenesis, the structure of sperm and egg, types of eggs, and the steps and significance of fertilisation.

महत्त्वाचे मुद्दे

• Gametogenesis has three phases: multiplication (mitosis), growth, and maturation (meiosis).
• Spermatogenesis occurs in the seminiferous tubules of the testes. Spermatogonia (2n) → primary spermatocytes (2n) → meiosis I → secondary spermatocytes (n) → meiosis II → spermatids (n) → spermiogenesis → spermatozoa.
• One primary spermatocyte gives four sperms.
• Sertoli cells nourish developing sperms; Leydig (interstitial) cells secrete testosterone.
• Oogenesis occurs in the ovary. It begins before birth; oogonia form primary oocytes that stay arrested in prophase I until puberty.
• One primary oocyte gives one ovum and two or three polar bodies (unequal division of cytoplasm).
• In humans, the secondary oocyte is released at ovulation, arrested at metaphase II; meiosis II completes only when a sperm enters.
• Sperm structure: head (nucleus + acrosome with enzymes like hyaluronidase), neck (centrioles), middle piece (mitochondria – energy), tail (flagellum for swimming).
• Egg coverings: primary (vitelline membrane, zona pellucida in mammals), secondary (follicle cells – corona radiata), tertiary (jelly coat in frog, albumen and shell in birds).
• Fertilisation in humans occurs in the ampulla of the fallopian tube.

महत्त्वाच्या संज्ञा

• Spermiogenesis – change of round spermatid into a tailed sperm (no division).
• Spermiation – release of sperms from Sertoli cells into the lumen.
• Graafian follicle – mature ovarian follicle with a fluid-filled antrum.
• Acrosome reaction – release of acrosomal enzymes that dissolve egg coverings.
• Cortical reaction – release of cortical granules that change the zona pellucida and block other sperms.
• Polyspermy – entry of more than one sperm; normally prevented.
• Capacitation – final activation of sperm in the female tract.
• Amphimixis – fusion of male and female pronuclei.

महत्त्वाची माहिती

• Types of eggs by yolk amount: microlecithal (little yolk; e.g. Amphioxus, eutherian mammals – often called alecithal), mesolecithal (moderate; frog), macrolecithal/megalecithal (much yolk; birds, reptiles).
• By yolk distribution: isolecithal / homolecithal (uniform), telolecithal (concentrated at the vegetal pole – frog, bird), centrolecithal (in the centre – insects).

५ महत्त्वाचे प्रश्न

Q1. What is the role of the acrosome?

The acrosome is a cap on the head of the sperm. It contains enzymes (like hyaluronidase and acrosin) that dissolve the coverings of the egg, helping the sperm to penetrate it.

Q2. Why does oogenesis give only one functional ovum?

During both meiotic divisions the cytoplasm divides unequally. Almost all of it goes to one cell (the ovum), so it has enough food for the embryo. The tiny polar bodies degenerate.

Q3. Describe spermatogenesis with a flow chart.

• Multiplication: spermatogonia divide by mitosis.
• Growth: primary spermatocytes (2n).
• Maturation: meiosis I → secondary spermatocytes (n); meiosis II → spermatids (n).
• Spermiogenesis: nucleus condenses, acrosome forms from Golgi, tail from centriole, mitochondria in middle piece.
• Hormonal control: FSH and LH (via testosterone).

Q4. Describe the structure of a human sperm with a labelled diagram.

• Head: nucleus (haploid) and acrosome.
• Neck: proximal and distal centrioles.
• Middle piece: mitochondrial spiral (energy for movement).
• Tail: axial filament (9 + 2 microtubules) covered by sheath.
• Labels: acrosome, nucleus, neck, centrioles, mitochondria, axial filament, tail.

Q5. Explain the process and significance of fertilisation.

• Sperm meets egg; capacitation; acrosome reaction.
• Sperm passes corona radiata and zona pellucida; membranes fuse.
• Cortical reaction blocks polyspermy.
• Secondary oocyte completes meiosis II; pronuclei fuse (amphimixis) → zygote.
• Significance: restores diploid number, brings variation, activates the egg, decides sex (in humans).

परीक्षेसाठी टीप

A comparison table of spermatogenesis and oogenesis is almost always asked. Draw both flow charts side by side with chromosome numbers.

थोडक्यात सारांश

After fertilisation, the zygote divides and develops into an embryo through a fixed series of stages: cleavage, blastulation, gastrulation and organogenesis. These early stages are studied in frog and chick as type examples. This topic covers types of cleavage, blastula, gastrula, germ layers and their derivatives, fate maps and foetal membranes.

महत्त्वाचे मुद्दे

• Cleavage – rapid mitotic divisions of the zygote without growth; the cells are called blastomeres. The embryo stays about the same size.
• Types of cleavage by plane/extent: holoblastic (whole egg divides; microlecithal and mesolecithal eggs) – equal (Amphioxus) or unequal (frog); meroblastic (only part divides; macrolecithal eggs) – discoidal (bird, reptile) or superficial (insects).
• Types by pattern: radial (echinoderms, amphibians), spiral (annelids, molluscs), bilateral, rotational (mammals).
• Determinate cleavage – fate of each blastomere fixed early; indeterminate – each early blastomere can form a whole embryo (basis of identical twins).
• Morula – solid ball of blastomeres (looks like a mulberry).
• Blastula – hollow ball with a cavity called the blastocoel. Frog blastula has small micromeres at the animal pole and large yolky macromeres at the vegetal pole. Chick has a blastoderm (area pellucida and area opaca). Mammals form a blastocyst with an inner cell mass and outer trophoblast.
• Gastrulation – movement of cells to form the three germ layers: ectoderm, mesoderm and endoderm. A new cavity, the archenteron (primitive gut), forms and opens by the blastopore.
• Morphogenetic movements: epiboly (spreading over), emboly – invagination, involution, convergence, divergence.
• In frog, gastrulation starts at the grey crescent (dorsal lip of blastopore). In chick, a primitive streak forms.
• Organogenesis – formation of organs from germ layers; neurulation forms the neural tube from ectoderm (neural plate → neural folds → neural tube).
• Spemann's organiser: Spemann and Mangold (1924) showed that the dorsal lip of the blastopore can induce a second embryo (primary organiser; embryonic induction).

महत्त्वाच्या संज्ञा

• Blastomere – a cell formed by cleavage.
• Blastocoel – cavity of the blastula.
• Archenteron – cavity of the gastrula; future gut.
• Yolk plug – yolky cells visible inside the circular blastopore of frog gastrula.
• Fate map – map showing what each region of the blastula will become (Vogt, using vital stains).
• Notochord – forms from chorda-mesoderm in the roof of the archenteron.
• Extra-embryonic (foetal) membranes – amnion, chorion, allantois, yolk sac (in reptiles, birds and mammals).

महत्त्वाची माहिती

• Foetal membranes: amnion (fluid cushion against shock and drying), chorion (gas exchange; forms placenta in mammals), allantois (stores waste in reptiles and birds; forms umbilical blood vessels in mammals), yolk sac (food in birds; early blood formation in mammals).

५ महत्त्वाचे प्रश्न

Q1. What is the grey crescent?

The grey crescent is a grey, crescent-shaped area that appears on the frog egg opposite the point of sperm entry, after cortical rotation. It marks the future dorsal side, and gastrulation begins here (dorsal lip of the blastopore).

Q2. Differentiate between holoblastic and meroblastic cleavage.

In holoblastic cleavage the whole egg divides completely, as in frog and Amphioxus. In meroblastic cleavage only the yolk-free cytoplasm divides, as a disc in bird eggs, because heavy yolk blocks division.

Q3. Describe cleavage and blastulation in frog.

• Mesolecithal, telolecithal egg; holoblastic, unequal, radial cleavage.
• First and second cleavage meridional; third latitudinal, above the equator.
• Micromeres at animal pole, macromeres at vegetal pole.
• Morula formed, then blastula with blastocoel in the animal half.
• Labels: animal pole, vegetal pole, micromeres, macromeres, blastocoel.

Q4. Explain gastrulation in frog.

• Begins at dorsal lip of blastopore (grey crescent).
• Epiboly: micromeres spread over macromeres.
• Invagination and involution of cells through the dorsal lip.
• Archenteron forms; blastocoel shrinks; yolk plug seen.
• Three germ layers: ectoderm, mesoderm (with chorda-mesoderm), endoderm.
• Labels: archenteron, blastopore, yolk plug, ectoderm, mesoderm, endoderm.

Q5. Describe the foetal membranes of chick and their functions.

• Amnion: encloses embryo in amniotic fluid; protection.
• Chorion: outer membrane; with allantois forms chorio-allantoic membrane for respiration.
• Allantois: stores nitrogenous waste (uric acid); respiration.
• Yolk sac: digests and absorbs yolk; blood formation.
• Draw a labelled diagram of the chick embryo with membranes.

परीक्षेसाठी टीप

Learn the derivatives table of germ layers – it gives quick marks. Always label animal and vegetal poles in frog diagrams.

थोडक्यात सारांश

The endocrine system is a group of ductless glands that release chemical messengers called hormones directly into the blood. Hormones act on distant target organs and control growth, metabolism, reproduction and homeostasis. This topic covers the human endocrine glands, their hormones, functions and disorders, the mechanism of hormone action and feedback control.

महत्त्वाचे मुद्दे

• Endocrine glands are ductless (अंतःस्रावी ग्रंथी). Hormones were named by Bayliss and Starling (secretin, 1902). Thomas Addison is called the father of endocrinology.
• Hormones may be peptides/proteins (insulin, growth hormone), steroids (cortisol, testosterone, oestrogen) or amino acid derivatives (thyroxine, adrenaline).
• Hypothalamus produces releasing and inhibiting hormones that control the anterior pituitary; it also makes oxytocin and ADH, stored in the posterior pituitary.
• Pituitary (hypophysis) is called the master gland: anterior lobe (adenohypophysis) and posterior lobe (neurohypophysis).
• Thyroid makes thyroxine (T₄) and T₃ (need iodine) and calcitonin.
• Parathyroid makes parathormone (PTH) which raises blood calcium.
• Adrenal cortex makes glucocorticoids (cortisol), mineralocorticoids (aldosterone) and sex hormones. Adrenal medulla makes adrenaline and noradrenaline – the "fight or flight" hormones.
• Pancreas (islets of Langerhans, described by Paul Langerhans): α-cells – glucagon (raises blood sugar); β-cells – insulin (lowers blood sugar); δ-cells – somatostatin. Banting and Best (1921) isolated insulin.
• Gonads: testes – testosterone; ovaries – oestrogen and progesterone.
• Pineal gland – melatonin (body clock, day–night rhythm). Thymus – thymosins (maturation of T-lymphocytes).
• Mechanism: protein hormones bind receptors on the cell membrane and act through second messengers like cyclic AMP (Sutherland); steroid hormones enter the cell, bind intracellular receptors and act on genes.
• Negative feedback keeps hormone levels steady (e.g. high thyroxine reduces TRH and TSH).

महत्त्वाच्या संज्ञा

• Target organ – organ on which a hormone acts.
• Tropic hormone – hormone that controls another endocrine gland (TSH, ACTH, FSH, LH).
• Second messenger – molecule inside the cell (cAMP, Ca²⁺) that carries the hormone signal.
• Homeostasis – maintenance of a steady internal environment.
• Goitre – enlarged thyroid, often due to iodine deficiency.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. Why is the pituitary called the master gland?

Its anterior lobe secretes tropic hormones (TSH, ACTH, FSH, LH, prolactin, GH) that control other endocrine glands like the thyroid, adrenal cortex and gonads. But it is itself controlled by the hypothalamus.

Q2. Differentiate between diabetes mellitus and diabetes insipidus.

Diabetes mellitus is due to lack of insulin or its action; blood sugar is high and glucose appears in urine. Diabetes insipidus is due to lack of ADH; large amounts of dilute urine are passed without sugar.

Q3. Describe the hormones of the anterior pituitary and their functions.

• GH (somatotropin): growth of bones and muscles.
• TSH: stimulates thyroid.
• ACTH: stimulates adrenal cortex.
• FSH: growth of follicles; spermatogenesis.
• LH (ICSH in males): ovulation, corpus luteum; testosterone secretion.
• Prolactin: milk production.
• Mention disorders of GH.

Q4. Explain the mechanism of hormone action.

• Hormone reaches target cell; binds a specific receptor.
• Peptide hormones: membrane receptor → G-protein → adenylate cyclase → cAMP → protein kinase → response (e.g. adrenaline breaking glycogen).
• Steroid hormones: pass membrane → bind cytoplasmic/nuclear receptor → hormone–receptor complex binds DNA → gene expression → new proteins.
• Draw both pathways as flow charts.

Q5. Describe the role of hormones in regulating blood sugar.

• Insulin (β-cells) lowers blood glucose: uptake by cells, glycogen formation in liver and muscle.
• Glucagon (α-cells) raises glucose: glycogen breakdown, gluconeogenesis.
• Adrenaline and cortisol also raise glucose during stress.
• Negative feedback keeps fasting glucose normal.
• Disorder: diabetes mellitus.

परीक्षेसाठी टीप

Learn a table of gland → hormone → function → disorder. It covers most short and long questions on this topic.

थोडक्यात सारांश

A nerve impulse is a wave of electrical change that travels along a nerve fibre. It is produced by the movement of sodium and potassium ions across the neuron membrane. At a synapse the impulse passes from one neuron to the next, usually through a chemical messenger. This topic covers the structure of a neuron, resting and action potentials, conduction in non-myelinated and myelinated fibres, and synaptic transmission.

महत्त्वाचे मुद्दे

• A neuron (चेतापेशी) has a cell body (cyton), short branched dendrites and a long axon. Many axons are covered by a myelin sheath formed by Schwann cells, with gaps called nodes of Ranvier.
• Resting membrane potential: the inside of a resting neuron is negative, about −70 mV, compared with the outside. The membrane is then polarised.
• It is maintained by the Na⁺–K⁺ pump (3 Na⁺ out, 2 K⁺ in), by the membrane being more permeable to K⁺ than Na⁺, and by large negative proteins inside.
• Action potential: a stimulus opens voltage-gated Na⁺ channels; Na⁺ rushes in and the inside becomes positive (about +30 to +40 mV) – depolarisation.
• Then Na⁺ channels close and K⁺ channels open; K⁺ flows out and the inside becomes negative again – repolarisation. A brief overshoot below −70 mV is hyperpolarisation.
• The stimulus must reach the threshold (about −55 mV). The impulse follows the all-or-none law: below threshold nothing happens, above it a full impulse is produced.
• During the refractory period the fibre cannot fire again; this keeps the impulse moving in one direction.
• In non-myelinated fibres, the impulse moves as a continuous wave through local currents – slow.
• In myelinated fibres, the impulse jumps from one node of Ranvier to the next – saltatory conduction – fast (up to about 100–120 m/s) and energy-saving.
• The ionic basis was worked out by Hodgkin and Huxley using the squid giant axon (Nobel Prize 1963).
• A synapse is the junction between two neurons. Most are chemical synapses: the impulse reaches the axon terminal → Ca²⁺ enters → synaptic vesicles release a neurotransmitter (e.g. acetylcholine) into the synaptic cleft → it binds receptors on the next neuron → ion channels open → new impulse.
• Acetylcholinesterase breaks down acetylcholine so the signal stops.
• Electrical synapses pass ions directly through gap junctions; they are faster but less common.

महत्त्वाच्या संज्ञा

• Polarisation – resting state with negative inside and positive outside.
• Depolarisation – inside becomes less negative or positive.
• Synaptic delay – short delay (about 0.5 ms) at a chemical synapse.
• EPSP / IPSP – excitatory or inhibitory postsynaptic potential.
• Neurotransmitter – chemical that carries the signal across a synapse (acetylcholine, noradrenaline, dopamine, serotonin, GABA).

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. State the all-or-none law.

A nerve fibre either does not respond to a stimulus below threshold, or gives a full-sized impulse to any stimulus at or above threshold. A stronger stimulus does not increase the size of the impulse; it only increases the frequency of impulses.

Q2. What is saltatory conduction?

In myelinated fibres the impulse jumps from one node of Ranvier to the next, because ion exchange occurs only at the nodes. This makes conduction much faster and saves energy.

Q3. Explain the ionic basis of resting and action potential.

• Distribution of Na⁺, K⁺ and proteins.
• Na⁺–K⁺ pump and K⁺ leak channels.
• Depolarisation, repolarisation, hyperpolarisation with voltage-gated channels.
• Threshold and refractory periods.
• Draw the action potential graph.

Q4. Describe the conduction of nerve impulse in myelinated and non-myelinated fibres.

• Structure of each fibre.
• Local current flow in non-myelinated fibres.
• Saltatory conduction in myelinated fibres.
• Comparison of speed and energy use; diagrams.

Q5. Describe the structure of a synapse and the mechanism of synaptic transmission.

• Presynaptic knob, vesicles, cleft, postsynaptic membrane, receptors.
• Steps of chemical transmission (Ca²⁺, exocytosis, binding, EPSP).
• Removal by acetylcholinesterase.
• Electrical synapses; properties (one-way, delay, fatigue).

परीक्षेसाठी टीप

Draw the action potential curve with labelled phases and voltages; it is asked almost every year in physiology papers.

थोडक्यात सारांश

Muscles move the body and its organs by contracting. Skeletal muscle is made of long fibres packed with protein filaments, actin and myosin, which slide over each other when the muscle contracts. This topic covers types of muscle, the ultrastructure of skeletal muscle, the sliding filament theory, the role of calcium and ATP, and properties such as twitch, tetanus, fatigue and rigor mortis.

महत्त्वाचे मुद्दे

• Types of muscle: skeletal (striated, voluntary, attached to bones), smooth (unstriated, involuntary, in gut and blood vessels) and cardiac (striated, involuntary, only in the heart, with intercalated discs).
• A skeletal muscle is made of bundles (fascicles) of muscle fibres. Each fibre is a long, multinucleated cell with a membrane called sarcolemma and cytoplasm called sarcoplasm.
• Each fibre has many myofibrils showing alternate dark A bands (anisotropic) and light I bands (isotropic).
• The unit of contraction is the sarcomere, the part between two Z lines.
• The A band contains thick myosin filaments; the I band contains thin actin filaments; the paler middle part of the A band is the H zone, with the M line at its centre.
• Thin filaments also carry tropomyosin and troponin, which block myosin-binding sites on actin at rest.
• Sliding filament theory was proposed in 1954 by H. E. Huxley and J. Hanson, and independently by A. F. Huxley and R. Niedergerke.
• Steps of contraction: nerve impulse reaches the neuromuscular junction → acetylcholine released → muscle action potential spreads along sarcolemma and T-tubules → sarcoplasmic reticulum releases Ca²⁺ → Ca²⁺ binds troponin → tropomyosin moves aside → myosin heads bind actin forming cross-bridges → ATP is split and myosin heads pull actin towards the M line (power stroke) → new ATP detaches the head and the cycle repeats.
• Relaxation: Ca²⁺ is pumped back into the sarcoplasmic reticulum, the binding sites are covered again and the filaments slide back.
• During contraction the I band and H zone shorten, the sarcomere shortens, but the A band length stays the same.
• Energy sources: ATP, creatine phosphate (quick refill), aerobic respiration, and anaerobic glycolysis giving lactic acid.

महत्त्वाच्या संज्ञा

• Motor unit – one motor neuron and all the muscle fibres it supplies.
• Muscle twitch – a single quick contraction to one stimulus.
• Tetanus – smooth, sustained contraction due to rapid repeated stimuli.
• Muscle fatigue – fall in contraction power after long activity, partly due to lactic acid.
• Oxygen debt – extra oxygen needed after exercise to remove lactic acid.
• Rigor mortis – stiffening of muscles after death because no ATP is left to detach myosin from actin.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. What is the role of calcium in muscle contraction?

Calcium released from the sarcoplasmic reticulum binds troponin. This shifts tropomyosin and exposes the myosin-binding sites on actin, so cross-bridges can form and contraction starts.

Q2. What is rigor mortis?

It is the stiffness of muscles a few hours after death. ATP is used up, so myosin heads stay attached to actin and muscles cannot relax.

Q3. Describe the ultrastructure of skeletal muscle.

• Muscle → fascicle → fibre → myofibril → sarcomere.
• Bands and lines: A, I, H, Z, M.
• Thick and thin filaments with their proteins.
• Sarcoplasmic reticulum and T-tubules (triad).
• Labelled diagram of a sarcomere.

Q4. Explain the sliding filament theory of muscle contraction.

• Proposers and year.
• Excitation at the neuromuscular junction.
• Excitation–contraction coupling and Ca²⁺.
• Cross-bridge cycle and role of ATP.
• Changes in bands; relaxation. Diagrams of relaxed and contracted sarcomere.

Q5. Compare skeletal, smooth and cardiac muscles.

• Shape, nuclei, striations, control, location.
• Special features: intercalated discs (cardiac), spindle shape (smooth).
• Speed of contraction and fatigue.
• Present as a table with diagrams.

परीक्षेसाठी टीप

Always state which bands shorten and which stay constant during contraction; it is a frequent objective question.

थोडक्यात सारांश

Sense organs contain receptors that change light, sound, gravity and movement into nerve impulses. The eye is the organ of sight, and the ear is the organ of both hearing and balance. This topic covers the structure of the human eye, the working of rods and cones, accommodation and eye defects, and the structure of the ear with the mechanisms of hearing and equilibrium.

महत्त्वाचे मुद्दे

• The eye (डोळा) is a nearly spherical organ in the bony orbit. Its wall has three layers.
• Outer fibrous layer: white, tough sclera; its transparent front part is the cornea.
• Middle vascular layer: choroid (blood vessels and pigment), ciliary body (holds the lens by suspensory ligaments) and iris (coloured, controls the size of the pupil).
• Inner layer: retina, with photoreceptors – rods and cones – and nerve cells.
• Rods (about 120 million) contain rhodopsin (visual purple) and work in dim light; they give black-and-white vision.
• Cones (about 6 million) contain iodopsin and work in bright light; they give colour vision. There are three kinds for red, green and blue.
• Fovea centralis (in the yellow spot) has only cones and gives the sharpest vision. The blind spot, where the optic nerve leaves, has no receptors.
• The lens divides the eye into the front chamber with watery aqueous humour and the back chamber with jelly-like vitreous humour.
• Accommodation: ciliary muscles change the curvature of the lens to focus near and far objects.
• Photochemistry: rhodopsin = opsin + 11-cis retinal (from vitamin A). Light changes it to all-trans retinal, rhodopsin splits and a nerve impulse starts. Vitamin A deficiency causes night blindness.
• The ear has three parts: external ear (pinna, auditory canal, ending at the tympanic membrane), middle ear (three ossicles – malleus, incus, stapes – and the Eustachian tube to the throat) and internal ear (membranous labyrinth filled with endolymph and surrounded by perilymph).
• Hearing: sound waves vibrate the tympanum → ossicles amplify → stapes pushes the oval window → fluid waves in the cochlea → the basilar membrane vibrates → hair cells of the organ of Corti bend against the tectorial membrane → impulses go by the auditory nerve to the brain. Humans hear about 20–20,000 Hz.
• Balance: the vestibular apparatus – three semicircular canals with cristae (detect rotation; dynamic balance) and the utricle and saccule with maculae carrying otoliths (detect head position and straight-line movement; static balance).

महत्त्वाच्या संज्ञा

• Photoreceptor – cell sensitive to light.
• Organ of Corti – hearing organ on the basilar membrane of the cochlea.
• Otoliths – small calcium carbonate crystals in the maculae.
• Eustachian tube – connects the middle ear with the pharynx and equalises air pressure.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. Distinguish between rods and cones.

Rods are rod-shaped, numerous, contain rhodopsin, work in dim light and do not detect colour. Cones are cone-shaped, fewer, contain iodopsin, work in bright light and give colour vision; they are packed in the fovea.

Q2. What is the function of the Eustachian tube?

It connects the middle ear cavity with the pharynx and keeps the air pressure equal on both sides of the eardrum, so that the eardrum vibrates freely and does not rupture.

Q3. Describe the structure of the human eye.

• Three coats and their parts.
• Lens, chambers and humours.
• Structure of retina; fovea and blind spot.
• Labelled diagram of vertical section of the eye.

Q4. Explain the mechanism of vision.

• Path of light and focusing; accommodation.
• Rhodopsin cycle with vitamin A.
• Generation of impulse and optic pathway to the brain.
• Colour vision by three types of cones.

Q5. Describe the structure of the ear and the mechanism of hearing and balance.

• External, middle and internal ear with diagram.
• Cochlea and organ of Corti.
• Steps of hearing.
• Static and dynamic equilibrium by maculae and cristae.

परीक्षेसाठी टीप

Practise the labelled diagrams of the eye (vertical section) and the cochlea (T.S.); a good diagram can secure half the marks of the long answer.

थोडक्यात सारांश

Ecology is the study of the relationships of organisms with each other and with their surroundings. The term was coined by Ernst Haeckel (1866). This topic covers ecological factors, population characteristics and growth, animal interactions, the structure and function of an ecosystem, food chains, ecological pyramids, biogeochemical cycles and environmental pollution.

महत्त्वाचे मुद्दे

• Ecology (परिस्थितिकी) – oikos = house, logos = study. Coined by Ernst Haeckel (1866).
• Levels of organisation: individual → population → community → ecosystem → biome → biosphere.
• Abiotic factors: temperature, light, water, humidity, soil, pH, salinity. Animals may be eurythermal (tolerate a wide temperature range) or stenothermal (narrow range).
• Liebig's law of minimum and Shelford's law of tolerance explain how limiting factors control distribution.
• Population attributes: density, natality (birth rate), mortality (death rate), age structure (pyramids), sex ratio, dispersion.
• Population growth: exponential (J-shaped curve) when resources are unlimited; logistic (S-shaped / sigmoid curve) when resources are limited and growth levels off at the carrying capacity (K).
• Interactions: mutualism (+/+), commensalism (+/0), parasitism (+/−), predation (+/−), competition (−/−), amensalism (−/0).
• Ecosystem (Tansley, 1935) = biotic + abiotic components. Producers, consumers and decomposers.
• Energy flow is one-way; Lindeman's 10% law – about 10% of energy passes to the next trophic level.
• Ecological pyramids: number, biomass and energy (pyramid of energy is always upright).
• Biogeochemical cycles: gaseous (carbon, nitrogen, oxygen) and sedimentary (phosphorus, sulphur).

महत्त्वाच्या संज्ञा

• Habitat – the place where an organism lives.
• Niche – the role and position of a species in its community.
• Carrying capacity (K) – maximum population an environment can support.
• Keystone species – a species with a very large effect on its community (e.g. tiger as top predator).
• Biomagnification – increase in concentration of a non-degradable toxin (e.g. DDT, mercury) at higher trophic levels.
• Eutrophication – nutrient enrichment of water bodies leading to algal blooms and oxygen depletion.
• BOD – biochemical oxygen demand; a measure of organic pollution in water.

सूत्रे

• Exponential growth: dN/dt = rN (r = intrinsic rate of natural increase, N = population size).
• Logistic growth: dN/dt = rN (K − N)/K.
• Population density = number of individuals ÷ area (or volume).
• Example: 600 deer live in a 30 km² forest. Density = 600 ÷ 30 = 20 deer per km².
• Growth rate example: a population of 1000 has 80 births and 30 deaths in a year (no migration). Net increase = 50; growth rate = 50/1000 = 0.05 per individual per year (5%).

५ महत्त्वाचे प्रश्न

Q1. Give two examples of mutualism.

Lichen (alga and fungus), and the termite with flagellate protozoa in its gut that digest wood. Both partners benefit in each case.

Q2. What is biomagnification?

Biomagnification is the increase in the concentration of a persistent toxic chemical, like DDT, at each higher level of a food chain. Top predators such as fish-eating birds get the highest amounts, which can thin their egg shells.

Q3. Compare exponential and logistic growth of a population.

• Exponential: unlimited resources; J-shaped; dN/dt = rN; no upper limit.
• Logistic: limited resources; S-shaped; dN/dt = rN(K − N)/K.
• Phases of the S-curve: lag, log (exponential), deceleration, stationary at K.
• Logistic is more realistic in nature.
• Draw both curves with axes labelled (population size vs time).

Q4. Describe the structure and function of a grassland ecosystem.

• Abiotic: soil, rainfall, light, temperature.
• Producers: grasses and herbs.
• Primary consumers: grasshoppers, rabbits, deer, cattle.
• Secondary/tertiary: frogs, snakes, foxes, hawks.
• Decomposers: bacteria and fungi.
• Food chain example and energy flow; nutrient cycling.

Q5. Explain the carbon cycle.

• CO₂ fixed by plants in photosynthesis.
• Passed to animals through food.
• Returned by respiration, decomposition and burning of fuels.
• Oceans store dissolved carbon; fossil fuels and limestone store carbon for long periods.
• Human activities increase CO₂ – greenhouse effect and global warming.
• Draw a cycle diagram.

परीक्षेसाठी टीप

Draw the J and S growth curves and the three ecological pyramids. Always give an Indian example for interactions and ecosystems.

थोडक्यात सारांश

DNA replication is the process by which a DNA molecule makes an exact copy of itself before cell division. Each new DNA molecule keeps one old strand and gets one new strand, so replication is semi-conservative. This topic covers the models of replication, the Meselson–Stahl experiment, the enzymes involved, and the steps of replication in prokaryotes with notes on eukaryotes.

महत्त्वाचे मुद्दे

• Replication (प्रतिकृती) takes place in the S phase of interphase.
• Three possible models: conservative (old molecule stays intact, new one fully new), semi-conservative (each daughter has one old and one new strand) and dispersive (old and new pieces mixed). Watson and Crick predicted the semi-conservative model.
• Meselson and Stahl (1958) proved semi-conservative replication in E. coli using heavy nitrogen (¹⁵N), light nitrogen (¹⁴N) and caesium chloride density-gradient centrifugation.
• Replication starts at a fixed point called the origin of replication (ori). E. coli has one origin; eukaryotic chromosomes have many.
• Unwinding forms a Y-shaped replication fork; replication usually proceeds in both directions (bidirectional) from the origin.
• Helicase unwinds the double helix by breaking hydrogen bonds; single-strand binding (SSB) proteins keep the strands apart; topoisomerase (DNA gyrase) relieves the tension ahead of the fork.
• Primase lays down a short RNA primer, because DNA polymerase cannot start a new chain by itself.
• DNA polymerase III (main enzyme in E. coli) adds nucleotides to the 3' end, so new DNA always grows in the 5' → 3' direction.
• The leading strand is made continuously towards the fork. The lagging strand is made discontinuously in short pieces called Okazaki fragments (discovered by Reiji Okazaki, 1968).
• DNA polymerase I removes RNA primers and fills the gaps with DNA; DNA ligase joins the fragments.
• DNA polymerases proofread (3' → 5' exonuclease activity) and remove wrong bases, so replication is very accurate.
• In eukaryotes the ends of linear chromosomes are completed by telomerase.

महत्त्वाच्या संज्ञा

• Template strand – the old strand read to make the new strand.
• Replicon – a unit of DNA replicated from one origin.
• Replication bubble (eye) – opened region between two forks.
• Primer – short RNA piece that provides a free 3'-OH end.
• Okazaki fragments – short DNA pieces of the lagging strand (about 1,000–2,000 nucleotides in bacteria).

महत्त्वाची माहिती

• Meselson–Stahl results: parent DNA (¹⁵N) = heavy band; after 1 generation in ¹⁴N = only hybrid (intermediate) band; after 2 generations = half hybrid, half light. This matches only the semi-conservative model.

५ महत्त्वाचे प्रश्न

Q1. Why is DNA replication called semi-conservative?

Because each daughter DNA molecule has one parental (old) strand and one newly made strand. Half of the original molecule is conserved in each daughter.

Q2. Why is the lagging strand made in pieces?

DNA polymerase can add nucleotides only in the 5' → 3' direction. On the lagging strand this direction is away from the fork, so short Okazaki fragments are made one by one and joined later by ligase.

Q3. Describe the Meselson–Stahl experiment.

• Growth of E. coli in ¹⁵NH₄Cl for many generations.
• Transfer to ¹⁴N medium.
• DNA extraction and CsCl centrifugation after each generation.
• Band positions and their interpretation.
• Diagram of the bands.

Q4. Explain the mechanism of DNA replication in prokaryotes.

• Initiation at oriC; unwinding by helicase; SSB and gyrase.
• Primer synthesis by primase.
• Elongation by DNA pol III; leading and lagging strands.
• Primer removal by pol I; joining by ligase.
• Termination; proofreading.
• Labelled diagram of replication fork.

Q5. Write a note on the enzymes of DNA replication.

• List each enzyme with its function (table above).
• Directionality of polymerases; proofreading.
• Telomerase in eukaryotes and its importance.

परीक्षेसाठी टीप

A neat replication fork diagram with leading strand, lagging strand, Okazaki fragments and enzymes labelled answers most questions on this topic.

थोडक्यात सारांश

Protein synthesis is the process by which the information in DNA is used to build proteins. It happens in two stages: transcription (DNA → mRNA) in the nucleus and translation (mRNA → protein) on ribosomes. This topic covers the central dogma, the genetic code, transcription and RNA processing, and the steps of translation.

महत्त्वाचे मुद्दे

• Central dogma (Francis Crick, 1958): DNA → RNA → protein. Information flows from DNA to RNA by transcription and from RNA to protein by translation. In some viruses RNA → DNA by reverse transcription.
• Transcription is carried out by RNA polymerase, using one DNA strand (the template or antisense strand) and making RNA in the 5' → 3' direction.
• In bacteria, the sigma (σ) factor of RNA polymerase recognises the promoter (the −10 Pribnow box TATAAT and the −35 region). Termination is either rho-dependent or rho-independent (hairpin loop).
• Eukaryotes have three RNA polymerases: I (rRNA), II (mRNA), III (tRNA and 5S rRNA).
• Processing of eukaryotic mRNA: a 5' cap (methyl guanosine) is added, a poly-A tail is added at the 3' end, and introns are removed while exons are joined (splicing).
• Genetic code: a triplet of bases (codon) codes for one amino acid. There are 64 codons: 61 code for amino acids and 3 are stop codons (UAA, UAG, UGA). AUG is the start codon (methionine).
• Properties of the code: triplet, non-overlapping, commaless, degenerate (most amino acids have more than one codon), universal (with a few exceptions), unambiguous.
• Nirenberg and Matthaei (1961) cracked the first codon: poly-U gave polyphenylalanine, so UUU = phenylalanine.
• Translation – activation: each amino acid is attached to its tRNA by aminoacyl-tRNA synthetase using ATP.
• Initiation: small ribosomal subunit binds mRNA; initiator tRNA (carrying formyl-methionine in bacteria, methionine in eukaryotes) pairs with AUG; large subunit joins.
• Elongation: the next aminoacyl-tRNA enters the A site; peptidyl transferase (an RNA enzyme, ribozyme) forms a peptide bond; the ribosome moves one codon (translocation); the empty tRNA leaves from the E site.
• Termination: a stop codon in the A site is recognised by release factors; the polypeptide is released and the ribosome separates.

महत्त्वाच्या संज्ञा

• Codon – three-base sequence on mRNA.
• Anticodon – complementary three-base sequence on tRNA.
• Exon / intron – coding / non-coding parts of a gene.
• Polysome – several ribosomes translating one mRNA at the same time.
• Wobble hypothesis (Crick, 1966) – the third base of a codon can pair loosely, so one tRNA can read more than one codon.

महत्त्वाची माहिती

• Ribosomes: prokaryotic 70S (50S + 30S); eukaryotic 80S (60S + 40S).

५ महत्त्वाचे प्रश्न

Q1. What is meant by degeneracy of the genetic code?

Most amino acids are coded by more than one codon. For example, leucine has six codons. This reduces the harmful effect of some point mutations.

Q2. What is splicing?

Splicing is the removal of non-coding introns from the primary RNA transcript and joining of the coding exons to form mature mRNA in eukaryotes.

Q3. Describe the process of transcription in prokaryotes.

• RNA polymerase structure (core enzyme + σ factor).
• Initiation at promoter; unwinding.
• Elongation in 5' → 3' direction.
• Termination: rho-dependent and rho-independent.
• Diagram of transcription unit.

Q4. Explain the steps of translation.

• Activation of amino acids.
• Initiation complex formation.
• Elongation: A, P and E sites; peptide bond; translocation.
• Termination and release.
• Diagrams.

Q5. Describe the properties of the genetic code.

• Triplet nature; 64 codons.
• Start and stop codons.
• Non-overlapping, commaless, degenerate, universal, unambiguous.
• Wobble hypothesis.
• Nirenberg's experiment.

परीक्षेसाठी टीप

Remember the three stop codons with the phrase "U Are Away, U Are Gone, U Go Away" (UAA, UAG, UGA).

थोडक्यात सारांश

Cells do not use all their genes all the time; they switch genes on and off as needed. This control of gene expression is called gene regulation. In bacteria, groups of related genes are controlled together as an operon. This topic covers the operon concept, the lac operon of E. coli with negative and positive control, a brief note on the trp operon, and an outline of gene regulation in eukaryotes.

महत्त्वाचे मुद्दे

• The operon model was proposed by François Jacob and Jacques Monod (1961), working on E. coli; they received the Nobel Prize in 1965.
• An operon is a group of structural genes with one promoter and one operator, transcribed together into one mRNA (polycistronic).
• Parts of the lac operon:
• Regulator gene (i / lacI) – makes the repressor protein; it has its own promoter and is always active.
• Promoter (p) – site where RNA polymerase binds.
• Operator (o) – site where the repressor binds; acts as an on–off switch.
• Structural genes: z (β-galactosidase – splits lactose into glucose and galactose), y (permease – brings lactose into the cell) and a (transacetylase).
• The lac operon is an inducible operon: it is normally off and turned on when lactose is present.
• Without lactose: the repressor binds the operator, blocks RNA polymerase, and the structural genes are not transcribed.
• With lactose: lactose (converted to allolactose, the true inducer) binds the repressor and changes its shape. The repressor can no longer bind the operator, so RNA polymerase transcribes z, y and a.
• When lactose is used up, the repressor becomes active again and the operon switches off. This is negative control.
• Positive control: when glucose is low, cAMP level rises; cAMP binds CAP (catabolite activator protein), and the CAP–cAMP complex helps RNA polymerase bind the promoter. When glucose is present, cAMP is low and the lac operon is weakly expressed even with lactose – catabolite repression. So E. coli uses glucose first.
• trp operon is a repressible operon: normally on; when tryptophan (the co-repressor) is plentiful it binds the inactive repressor, which then binds the operator and switches the operon off.
• Eukaryotic regulation works at many levels: chromatin packing, transcription factors, enhancers and silencers, RNA processing, mRNA stability and translation.

महत्त्वाच्या संज्ञा

• Inducer – small molecule that switches on an inducible operon (allolactose).
• Co-repressor – small molecule that activates a repressor (tryptophan).
• Polycistronic mRNA – one mRNA carrying information for several proteins.
• Constitutive gene – gene expressed all the time (housekeeping gene).
• Catabolite repression – glucose preventing use of other sugars.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. What is an operon?

An operon is a unit of gene expression in bacteria consisting of a promoter, an operator and a group of structural genes that work together and are transcribed as one mRNA.

Q2. What is the role of the repressor in the lac operon?

The repressor, made by the regulator gene, binds to the operator when lactose is absent and blocks RNA polymerase, so the structural genes stay switched off.

Q3. Describe the lac operon with its negative control.

• Proposers and organism.
• Parts and their roles.
• Absence and presence of lactose (with diagrams).
• Switching off when lactose is used.

Q4. Explain positive control of the lac operon.

• Role of glucose, cAMP and CAP.
• CAP–cAMP binding site near the promoter.
• Catabolite repression and diauxic growth.
• Table of conditions.

Q5. Distinguish between inducible and repressible operons with examples.

• Definitions.
• Lac operon as inducible; trp operon as repressible with diagrams.
• Table of differences.

परीक्षेसाठी टीप

Draw two diagrams for the lac operon: "lactose absent" and "lactose present". Label repressor, operator, promoter and the three structural genes.

थोडक्यात सारांश

Animal biotechnology uses animal cells, genes and reproductive techniques to make useful products and improve animals and human health. This topic covers animal cell culture, recombinant DNA technology, transgenic animals, cloning (Dolly), artificial insemination and embryo transfer, monoclonal antibodies, gene therapy, DNA fingerprinting and ethical issues.

महत्त्वाचे मुद्दे

• Animal cell culture: growing animal cells outside the body in a sterile, nutrient medium at about 37 °C with 5% CO₂, in a CO₂ incubator. The medium has salts, glucose, amino acids, vitamins and usually serum (e.g. foetal bovine serum). Work is done in a laminar air flow cabinet.
• Primary culture comes directly from tissue; a cell line can be sub-cultured many times. HeLa cells (from Henrietta Lacks, 1951) were the first continuous human cell line.
• rDNA technology tools: restriction enzymes, DNA ligase, vectors (plasmids, viruses), host cells; gene products like human insulin (Humulin, made in E. coli; Eli Lilly, 1983), growth hormone, interferons and vaccines (hepatitis B vaccine made in yeast).
• Transgenic animals carry a foreign gene. Example: Rosie, the first transgenic cow (1997), produced milk with human alpha-lactalbumin. Transgenic mice are used as disease models.
• Cloning: Dolly the sheep (born 1996, announced 1997) was the first mammal cloned from an adult cell by somatic cell nuclear transfer, by Ian Wilmut and team at the Roslin Institute, Scotland.
• Artificial insemination (AI): semen from a superior bull is collected, stored frozen in liquid nitrogen (−196 °C) and placed into the female's tract. Widely used for cattle and buffalo improvement in India.
• MOET (Multiple Ovulation Embryo Transfer): a cow is given FSH-like hormones for superovulation, mated or inseminated, embryos (8–32 cell stage) are collected and transferred to surrogate mothers.
• Monoclonal antibodies: made by hybridoma technology (Köhler and Milstein, 1975) – fusing an antibody-making B-cell with a myeloma (cancer) cell.
• Gene therapy: correcting a defective gene by inserting a normal gene. The first clinical gene therapy (1990) was for ADA (adenosine deaminase) deficiency.
• DNA fingerprinting: developed by Alec Jeffreys (1984–85); based on VNTRs (variable number tandem repeats). In India, Dr. Lalji Singh (CCMB, Hyderabad) is called the father of Indian DNA fingerprinting.

महत्त्वाच्या संज्ञा

• Transgenic – organism with a foreign gene in its genome.
• Somatic cell nuclear transfer – putting a body-cell nucleus into an enucleated egg.
• Hybridoma – fused cell that makes one specific antibody and divides endlessly.
• Southern blotting – technique to detect specific DNA sequences (E. M. Southern).
• Stem cells – unspecialised cells that can divide and form many cell types (embryonic and adult).
• Biopiracy – use of biological resources or traditional knowledge without permission or fair payment (e.g. patent disputes on turmeric and neem).

महत्त्वाची माहिती

• Ethical issues: animal welfare, safety of GM products, misuse of cloning, gene patenting. In India, the GEAC (Genetic Engineering Appraisal Committee) checks the safety of GM research and products.

५ महत्त्वाचे प्रश्न

Q1. What is a transgenic animal? Give an example.

A transgenic animal has a foreign gene deliberately inserted into its genome and passes it to offspring. Example: Rosie, a transgenic cow whose milk contained human alpha-lactalbumin.

Q2. What are monoclonal antibodies?

Monoclonal antibodies are identical antibodies made by a single clone of hybridoma cells. They bind one specific antigen and are used in pregnancy tests, diagnosis and cancer treatment.

Q3. Explain how Dolly the sheep was cloned.

• Udder (mammary) cell taken from a Finn Dorset ewe; grown in low-nutrient culture.
• Egg taken from a Scottish Blackface ewe; nucleus removed.
• Udder cell fused with the empty egg by an electric pulse.
• Embryo grown and placed in a surrogate ewe.
• Dolly born genetically identical to the udder-cell donor.

Q4. Describe DNA fingerprinting and its applications.

• Isolate DNA from blood, hair roots, semen etc.; amplify by PCR if needed.
• Cut with restriction enzymes; separate by gel electrophoresis.
• Southern blotting onto a membrane; hybridise with labelled VNTR probes.
• Autoradiography shows a band pattern unique to each person (except identical twins).
• Uses: crime investigation, paternity disputes, identifying bodies, wildlife forensics.

Q5. Give the steps of animal cell culture.

• Collect tissue aseptically; cut into small pieces.
• Disaggregate cells with trypsin (enzymatic) or mechanically.
• Seed cells in culture flasks with medium and serum.
• Incubate at 37 °C, 5% CO₂, high humidity.
• Sub-culture when confluent; maintain cell lines; store frozen.
• Uses: vaccines, drug testing, cancer research.

परीक्षेसाठी टीप

Learn the names and years in the table. For ethics, write both benefits and concerns in a balanced way.

थोडक्यात सारांश

Helminths are parasitic worms belonging to flatworms (Platyhelminthes) and roundworms (Nematoda). Many of them live in the human body and cause serious diseases, especially where sanitation is poor. This topic covers the host–parasite relationship and parasitic adaptations, followed by important helminths of man – Wuchereria, Ancylostoma, Enterobius, Dracunculus, Echinococcus and Fasciola – with their mode of infection, disease and control.

महत्त्वाचे मुद्दे

• Parasitism: a close relationship in which one organism (parasite) lives on or in another (host) and harms it.
• Definitive host – where the parasite becomes adult and reproduces sexually; intermediate host – where larval stages develop.
• Adaptations of endoparasites: loss or reduction of locomotory and sense organs; thick cuticle or tegument resistant to digestive enzymes; hooks and suckers for attachment; anaerobic respiration; very high reproductive capacity; often hermaphrodite (flatworms); complex life cycles with more than one host.
• Wuchereria bancrofti (filarial worm): adults live in lymph vessels and nodes. Female releases microfilariae that circulate in blood mostly at night (nocturnal periodicity). Vector: **female Culex mosquito. Disease: filariasis, leading to elephantiasis** (swelling of legs, scrotum) and hydrocele. Many districts of Vidarbha are endemic.
• Ancylostoma duodenale (hookworm): lives in the small intestine, attaching by cutting plates and sucking blood. Infection: filariform larvae penetrate the skin of bare feet ("ground itch"). Causes severe anaemia and weakness.
• Enterobius vermicularis (pinworm/threadworm): common in children; lives in the large intestine. Female lays eggs at night around the anus, causing itching; scratching leads to autoinfection.
• Dracunculus medinensis (guinea worm): infection by drinking water with infected Cyclops. The female emerges from a painful blister on the leg. India was declared guinea-worm free in 2000.
• Echinococcus granulosus (dog tapeworm): adult in dog's intestine; man gets eggs from dog faeces and becomes an accidental intermediate host, developing hydatid cysts in the liver or lungs.
• Fasciola hepatica (liver fluke): mainly in sheep and cattle, occasionally in man; snail (Lymnaea) is the intermediate host; infection by eating aquatic plants with metacercariae.

महत्त्वाच्या संज्ञा

• Vector – organism that carries a parasite from one host to another.
• Microfilaria – larva of the filarial worm in blood.
• Autoinfection – reinfection of the same host by its own parasite's eggs.
• Hydatid cyst – fluid-filled larval cyst of Echinococcus.
• Zoonosis – disease passed from animals to humans.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. What is nocturnal periodicity?

It is the appearance of microfilariae of Wuchereria in the peripheral blood mainly at night (about 10 pm to 2 am), the time when the Culex vector bites. Blood samples for diagnosis are therefore taken at night.

Q2. How does hookworm infection occur?

Hookworm eggs pass out in faeces and hatch in moist soil. Their filariform larvae penetrate the skin of a person walking barefoot, travel through blood and lungs, and reach the small intestine.

Q3. Describe parasitic adaptations in helminths.

• Morphological: cuticle/tegument, hooks, suckers, loss of organs.
• Physiological: anaerobic respiration, anti-enzymes, osmotic adjustment.
• Reproductive: hermaphroditism, huge egg output, larval multiplication.
• Life-cycle adaptations: intermediate hosts, vectors.

Q4. Describe the life cycle and pathogenicity of Wuchereria bancrofti.

• Structure of adult and microfilaria.
• Development in mosquito (L1 → L3) and transmission.
• Development in man.
• Symptoms, diagnosis, treatment (DEC) and control (mosquito control, mass drug administration).

Q5. Write short notes on Ancylostoma and Enterobius.

• Habitat, structure, mode of infection, life cycle.
• Disease symptoms.
• Prevention: wearing footwear, sanitation, hygiene, deworming.

परीक्षेसाठी टीप

Learn one table of parasite, host, mode of infection and disease; it answers most short notes and matching questions.

थोडक्यात सारांश

Sericulture is the rearing of silkworms for the production of raw silk. India is the second largest producer of silk in the world after China, and the only country that produces all four commercial kinds of silk: mulberry, tasar, eri and muga. This topic covers types of silkworms, the life cycle of Bombyx mori, mulberry cultivation, rearing methods, cocoon processing, diseases and the economic value of sericulture.

महत्त्वाचे मुद्दे

• The word comes from "sericos" (Greek for silk). Sericulture is रेशीम उद्योग in Marathi.
• Silk is a natural protein fibre made of fibroin (inner core) and sericin (outer gum).
• Types of silk and silkworms:
• Mulberry silk – Bombyx mori; feeds on mulberry (Morus alba). Most important (bulk of India's silk).
• Tasar (tussar) silk – Antheraea mylitta (tropical tasar) on Terminalia (arjun, ain) and Shorea robusta (sal). Grown in forest areas including Vidarbha (Bhandara, Gondia, Chandrapur, Gadchiroli).
• Eri silk – Samia ricini (Philosamia ricini) on castor leaves. Eri is spun from opened cocoons, so it is called "ahimsa silk".
• Muga silk – Antheraea assamensis on som and soalu trees; golden-yellow silk found only in Assam.
• Bombyx mori is a fully domesticated insect; it cannot survive in the wild.
• **Life cycle of Bombyx mori: egg → larva (caterpillar) → pupa (inside cocoon) → adult moth. Complete metamorphosis** (holometabolous).
• Larva grows through five instars with four moults; the final instar stops feeding and spins a cocoon.
• Silk is secreted by a pair of silk glands (modified salivary glands) and comes out through the spinneret.
• One cocoon has a single continuous filament, often about 1000–1500 m long (varies with breed).

महत्त्वाच्या संज्ञा

• Moriculture – cultivation of mulberry plants.
• Instar – larval stage between two moults.
• Spinning – making the cocoon by laying silk thread in a figure-of-eight pattern.
• Stifling – killing the pupa inside the cocoon by heat (sun drying, steam or hot air) to keep the filament unbroken.
• Reeling – unwinding silk filaments from cooked cocoons to make raw silk.
• Degumming – removing sericin to make silk soft and shiny.
• Disease-free layings (DFLs) – eggs from tested, healthy moths.
• Voltinism – number of generations per year: univoltine (one), bivoltine (two), multivoltine (many).

महत्त्वाची माहिती

• Rearing: chawki (young-age) rearing of 1st–2nd instars with tender leaves; late-age rearing on mature leaves; temperature about 23–28 °C and humidity about 70–85% (varies by stage); mountages (chandrikes) for spinning.
• Diseases of silkworm: pebrine (protozoan Nosema bombycis; studied by Louis Pasteur), flacherie (bacteria/virus; flaccid larvae), grasserie (nuclear polyhedrosis virus; milky fluid, swollen body), muscardine (fungus Beauveria bassiana; larva becomes hard and chalky).
• Pest: uzi fly (Exorista bombycis) lays eggs on larvae.
• By-products: silk waste for spun silk, pupae as poultry/fish feed and oil, mulberry for fodder.
• Central Silk Board (Bengaluru) oversees sericulture in India; Karnataka is the leading mulberry silk state.

५ महत्त्वाचे प्रश्न

Q1. What are fibroin and sericin?

Fibroin is the insoluble protein forming the inner core of the silk filament. Sericin is the gummy protein coating that sticks the filaments together; it is removed by degumming.

Q2. Name the four types of silk produced in India with their silkworms.

Mulberry (Bombyx mori), tasar (Antheraea mylitta), eri (Samia ricini) and muga (Antheraea assamensis).

Q3. Describe the life cycle of Bombyx mori.

• Egg: laid in clusters on mulberry leaves or paper; hatches in about 10 days (non-hibernating).
• Larva: five instars, four moults; voracious feeding on mulberry leaves.
• Spinning: mature larva secretes silk from silk glands; cocoon formed in 2–3 days.
• Pupa: inside cocoon.
• Adult: moth comes out by softening cocoon with alkaline fluid; does not feed; mates and lays eggs.
• Draw labelled stages.

Q4. Explain the processing of cocoons.

• Harvest and sorting of cocoons.
• Stifling to kill pupae.
• Cooking in hot water to soften sericin.
• Reeling: filaments of several cocoons combined into one raw silk thread.
• Re-reeling, twisting (throwing), degumming, dyeing, weaving.

Q5. Describe the diseases of silkworm and their control.

• Pebrine: Nosema bombycis; dark spots, uneven growth; control by mother moth examination and DFLs.
• Flacherie: soft, flaccid larvae; hygiene, good leaves.
• Grasserie: virus; swollen segments, milky fluid; disinfection.
• Muscardine: Beauveria bassiana; mummified larvae; dusting with lime/ disinfectants, low humidity.
• General: disinfection of rearing house, proper spacing, temperature and humidity control.

परीक्षेसाठी टीप

Remember all four silks with silkworm names and food plants. Mention tasar silk of Vidarbha as a local example.

थोडक्यात सारांश

Apiculture (bee-keeping) is the rearing and management of honey bees for honey, wax and other products, and for pollination of crops. Honey bees are social insects that live in colonies with clear division of labour. This topic covers Indian species of honey bees, the bee colony, life cycle, communication, modern bee-keeping methods, bee products, enemies and diseases.

महत्त्वाचे मुद्दे

• Apiculture comes from Apis (bee). Bee-keeping is मधुमक्षिका पालन in Marathi.
• Honey bees of India:
• Apis dorsata – rock bee; largest; builds a single huge comb in the open on trees, cliffs and buildings; aggressive; gives the most honey per comb but cannot be domesticated.
• Apis cerana indica – Indian hive bee; builds several parallel combs in dark cavities; gentle; domesticated in boxes.
• Apis florea – little bee; smallest; single small comb on bushes; little honey.
• Apis mellifera – European (Italian) bee; introduced; high yield; gentle; widely kept in modern apiaries.
• Stingless bees (Trigona) also give small amounts of honey.
• Castes in a colony:
• Queen – one fertile female; largest; lays eggs (up to about 1500–2000 eggs a day in peak season); develops from a fertilised egg fed only royal jelly.
• Drones – fertile males from unfertilised eggs (parthenogenesis); die after mating; do no other work.
• Workers – sterile females; do all work: cleaning, feeding larvae (nurse bees), building comb, guarding, collecting nectar and pollen (foragers).
• Life cycle: complete metamorphosis – egg → larva → pupa → adult. Development time is about 16 days for the queen, 21 days for the worker and 24 days for the drone.
• Nuptial flight – the queen mates with several drones in the air and stores sperm for life.
• Communication (dance language) was explained by Karl von Frisch (Nobel Prize 1973): the round dance shows food near the hive; the waggle (tail-wagging) dance shows direction and distance of distant food.

महत्त्वाच्या संज्ञा

• Royal jelly – protein-rich secretion of the hypopharyngeal glands of young workers.
• Swarming – old queen leaves with part of the colony to form a new colony.
• Absconding – whole colony leaves the hive due to disturbance, disease or lack of food.
• Propolis – sticky resin collected from plants; used to seal gaps in the hive.
• Bee venom – secretion from the sting gland; used in some medicines.
• Honey extractor – machine that removes honey from combs by centrifugal force without damaging them.

महत्त्वाची माहिती

• Modern (movable-frame) hive, based on Langstroth (1851), has: stand, bottom board, brood chamber with frames, queen excluder, super chamber (honey frames), inner cover and top cover. Comb foundation sheets of beeswax help bees build straight combs.
• Bee-keeping equipment: smoker, bee veil, gloves, hive tool, uncapping knife, honey extractor, queen cage.
• Products: honey (mainly fructose and glucose with water, enzymes and minerals), beeswax (from wax glands on the worker's abdomen; used in cosmetics, candles, polishes), royal jelly, propolis, pollen, venom.
• Pollination: bees greatly increase yield of crops like sunflower, mustard, apples and many fruits.
• Enemies: wax moth (Galleria mellonella), mites (Varroa), ants, wasps, bee-eater birds. Diseases: Thai sacbrood virus (serious in Apis cerana), foulbrood (bacterial), nosema (Nosema protozoan/microsporidian).

५ महत्त्वाचे प्रश्न

Q1. What is royal jelly?

Royal jelly is a creamy, protein-rich food secreted by the glands of young worker bees. All larvae get it for the first few days, but only the queen larva is fed on it throughout, which makes her develop into a fertile queen.

Q2. Why is the drone called the son of an unmarried mother?

A drone develops from an unfertilised egg laid by the queen (parthenogenesis). So it has a mother (the queen) but no father.

Q3. Describe the social organisation of a honey bee colony.

• Queen: egg laying; controls colony with pheromones.
• Drones: mating only.
• Workers: age-based duties – cleaners, nurses, wax builders, guards, foragers.
• Division of labour ensures survival.
• Communication by dances and pheromones.

Q4. Describe the structure of a modern bee hive (Langstroth type).

• Stand and bottom board with entrance.
• Brood chamber with movable frames for egg laying.
• Queen excluder to keep queen out of the super.
• Super chamber for honey storage.
• Inner cover and top cover (roof).
• Advantages: easy inspection, honey extraction without killing bees, reuse of combs.

Q5. Give the economic importance of apiculture.

• Honey as food and medicine.
• Beeswax for cosmetics, candles, polish, foundation sheets.
• Royal jelly, propolis, pollen, venom.
• Pollination increases crop yield and quality.
• Self-employment for rural people; low investment (supported by KVIC and the National Bee Board).

परीक्षेसाठी टीप

Learn the four Apis species and the castes with their origin (fertilised or unfertilised eggs). The waggle dance by von Frisch is a favourite short note.

थोडक्यात सारांश

Lac culture is the rearing of the lac insect on host trees to obtain lac, a natural resin. Vermiculture is the rearing of earthworms to turn organic waste into rich manure called vermicompost. Both are low-cost, eco-friendly rural industries suited to Vidarbha and other parts of Maharashtra. This topic covers the lac insect, its life cycle, host plants, cultivation and products, and the species, method and benefits of vermicomposting.

महत्त्वाचे मुद्दे

• Lac insect: Kerria lacca (earlier Laccifer lacca), a scale insect of order Hemiptera. Lac is लाख in Marathi.
• Lac is a resin secreted by the female through glands on its body as a protective covering. Females are degenerate, sac-like and stay fixed on twigs; males are smaller and some are winged.
• Life cycle: eggs hatch inside the female's cell (it is ovoviviparous) → red crawlers (nymphs) come out in large numbers (swarming) → settle on tender twigs and suck sap → secrete lac → moult and become adults → mating → each female produces a few hundred young. Two generations a year.
• Host plants: kusum (Schleichera oleosa), palas (Butea monosperma), ber (Ziziphus mauritiana), and others.
• Strains and crops: Kusmi strain (on kusum) gives the Aghani and Jethwi crops; Rangeeni strain (on palas, ber) gives the Katki and Baisakhi crops.
• Cultivation steps: pruning of host trees → inoculation by tying brood lac (twigs with mature females about to release crawlers) on fresh shoots → removal of brood lac after swarming → crop care → harvesting by cutting lac-encrusted twigs (stick lac).
• Processing: stick lac → scraping and crushing → washing → seed lac → melting and filtering → shellac.
• Uses: varnishes and polishes, sealing wax, electrical insulation, printing inks, coating of fruits and tablets, cosmetics, bangles, and lac dye.
• Enemies: predator moths such as Eublemma amabilis, and chalcid parasitoids.
• India is the world's leading lac producer (Jharkhand, Chhattisgarh, Madhya Pradesh, and Gondia–Bhandara belt of Maharashtra). The ICAR–Indian Institute of Natural Resins and Gums, Ranchi (founded 1925 as the Indian Lac Research Institute) guides lac research.
• Vermiculture: surface-living earthworms are used – Eisenia fetida (red wiggler), Eudrilus eugeniae (African nightcrawler) and Perionyx excavatus.
• Vermicomposting method: shaded pit, tank or bed → bottom layer of bricks or coarse material for drainage → bedding of dry leaves and soil → half-decomposed cow dung and organic waste → release of earthworms (about 1 kg per square metre) → cover with gunny bag → keep moist (about 50–60%) and cool (about 20–30 °C) → compost ready in about 45–60 days → stop watering, worms move down, harvest the upper compost and sieve.

महत्त्वाच्या संज्ञा

• Brood lac – lac-bearing twigs used as "seed" for new infection.
• Swarming – mass emergence of crawlers from the mother cells.
• Shellac – purified, flaked form of lac.
• Vermicompost – earthworm castings mixed with decomposed organic matter.
• Vermiwash – liquid collected from a vermicompost unit, used as a foliar spray.

महत्त्वाची माहिती

• Benefits of vermiculture: recycles farm and kitchen waste, reduces chemical fertiliser use, low cost, gives rural employment.

५ महत्त्वाचे प्रश्न

Q1. What is brood lac?

Brood lac is a piece of twig carrying mature female lac insects that are about to release crawlers. It is tied to a new host tree so that the crawlers settle on fresh shoots; this is called inoculation.

Q2. Name two earthworm species used in vermiculture.

Eisenia fetida (red wiggler) and Eudrilus eugeniae (African nightcrawler). Perionyx excavatus is an Indian species also used.

Q3. Describe the life cycle of the lac insect.

• Female and male structure.
• Eggs, crawlers, swarming, settling.
• Lac secretion, moulting, maturity, mating.
• Two generations per year; draw the life cycle.

Q4. Explain the methods of lac cultivation and its economic importance.

• Host plants and strains; crops.
• Pruning, inoculation, crop care, harvesting.
• Processing to shellac.
• Uses; enemies and their control; lac industry in India.

Q5. Describe the method of vermicomposting and its advantages.

• Selection of species and site.
• Preparation of bed; layers; conditions.
• Maintenance and harvesting.
• Advantages to soil, farmers and environment.

परीक्षेसाठी टीप

Learn the four crop names with their strains (Kusmi: Aghani, Jethwi; Rangeeni: Katki, Baisakhi); they are favourite objective questions in applied zoology.

थोडक्यात सारांश

Aquaculture is the farming of aquatic organisms – fish, prawns, crabs, mussels and seaweeds – in controlled conditions in fresh, brackish or sea water. India is one of the world's leading producers of farmed fish. This topic covers types of aquaculture, composite fish culture of Indian major carps, induced breeding, pond management, prawn and pearl culture, and the Blue Revolution.

महत्त्वाचे मुद्दे

• Aquaculture includes fish culture (pisciculture), prawn culture, pearl culture, crab culture and seaweed culture. Fish farming is मत्स्यपालन / मत्स्यशेती in Marathi.
• Types by water: freshwater (ponds, tanks, reservoirs), brackish water (estuaries, coastal ponds) and mariculture (sea).
• Types by intensity: extensive (low input, natural food), semi-intensive (some feeding and fertilising), intensive (high stocking, full feeding, aeration).
• Indian major carps (IMC): catla (Catla catla) – surface feeder; rohu (Labeo rohita) – column feeder; mrigal (Cirrhinus mrigala) – bottom feeder.
• Exotic carps: silver carp (Hypophthalmichthys molitrix) – surface (phytoplankton) feeder; grass carp (Ctenopharyngodon idella) – feeds on aquatic weeds; common carp (Cyprinus carpio) – bottom feeder.
• Composite fish culture: six compatible species (3 Indian + 3 exotic carps) are reared together in one pond so they use food at all levels without competing; it gives much higher yield.
• Induced breeding (hypophysation): carps do not breed in stagnant ponds, so they are injected with pituitary gland extract from mature fish (or synthetic hormone preparations such as Ovaprim) to make them spawn. India's pioneers in this method include Dr. Hiralal Chaudhuri (1957), called the father of induced breeding in India.
• Pond types in a fish farm: breeding pond (hapa), hatching pond, nursery pond, rearing pond and stocking pond.
• Stages of fish seed: spawn (just hatched) → fry → fingerling.
• Blue Revolution – rapid increase in fish production through aquaculture. The Government of India launched the "Blue Revolution" scheme (2015–16) and the PM Matsya Sampada Yojana (2020).

महत्त्वाच्या संज्ञा

• Hapa – rectangular cloth net enclosure fixed in a pond for breeding fish.
• Liming – adding lime to correct soil pH and kill pests.
• Manuring – adding cow dung or fertilisers to grow plankton (natural fish food).
• Eradication of predators – removing predatory and weed fish (e.g. with mahua oil cake) before stocking.
• Stocking density – number of fish seed released per unit area.
• Brackish water – mix of fresh and salt water, found in estuaries.

महत्त्वाची माहिती

• Prawn culture: freshwater giant prawn Macrobrachium rosenbergii; brackish/marine tiger prawn Penaeus monodon and whiteleg shrimp Litopenaeus vannamei (widely farmed in coastal India).
• Pearl culture: pearl oyster Pinctada fucata (marine); freshwater mussel Lamellidens used for freshwater pearls. A small nucleus is surgically placed with mantle tissue; nacre layers form the pearl. The CMFRI (Central Marine Fisheries Research Institute) developed pearl culture technology in India (Tuticorin).
• Fish diseases: epizootic ulcerative syndrome (EUS), fin rot, gill rot, white spot (Ichthyophthirius), argulosis (fish louse Argulus).
• Research institutes: CIFA (Bhubaneswar, freshwater aquaculture), CIFE (Mumbai, fisheries education), CMFRI (Kochi).

५ महत्त्वाचे प्रश्न

Q1. What is composite fish culture?

Composite fish culture is rearing several compatible fish species with different feeding habits (usually 3 Indian and 3 exotic carps) together in one pond. All food niches are used and fish do not compete, so yield increases.

Q2. Name the Indian major carps and their feeding zones.

Catla (Catla catla) feeds at the surface, rohu (Labeo rohita) in the column, and mrigal (Cirrhinus mrigala) at the bottom.

Q3. Describe the method of induced breeding in carps.

• Select healthy, mature male and female brood fish.
• Collect pituitary glands from mature donor fish; prepare extract (or use synthetic hormone).
• Inject female (two doses) and male (one dose) intramuscularly near the dorsal fin or tail base.
• Release in breeding hapa; spawning occurs in a few hours.
• Collect fertilised eggs; transfer to hatching hapas/ hatchery; spawn hatch in about 15–18 hours (temperature-dependent).

Q4. Explain the management of a fish pond.

• Pre-stocking: draining/drying, removing weeds and predatory fish, liming, manuring.
• Stocking: right species and density of fingerlings.
• Post-stocking: supplementary feed (rice bran + oil cake), fertilising, checking water quality (oxygen, pH), disease control.
• Harvesting at marketable size.

Q5. Give the importance of aquaculture.

• Cheap source of animal protein.
• Employment and income in rural and coastal areas.
• Export earnings (shrimp).
• Use of waste land and water bodies; integrated farming with ducks, poultry or paddy.
• By-products: fish oil, fish meal, manure.

परीक्षेसाठी टीप

Learn the feeding zone table of six carps – it is the heart of composite fish culture questions. Always write scientific names in italics.